Downhole oilfield erosion protection of a jet pump throat by operating the jet pump in cavitation mode

ABSTRACT

A method of improving erosion performance (decreasing the erosion) of components—such as a throat, a nozzle, or a diffuser—for a downhole tool used for cleaning a wellbore is disclosed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the cleaning of wellbores in the fieldof oil and gas recovery. More particularly, this invention relates to adevice adapted to improve the erosion performance of components utilizedin the removal of solid particulate matter from a well.

2. Description of the Related Art

In the oil and gas industry, wellbores often become plugged with sand,filter cake, or other hard particulate solids, which need to be removedperiodically to improve oil production. Prior art methods for cleaningthe wellbore and the removal of these particulate solids include pumpinga fluid from the surface to the area to be cleaned. To effectively cleanthe solids from the wellbore, the pumped fluids must return to surface,thereby establishing circulation. Therefore, the bottom of the holecirculating pressure must be high enough to support circulation but lowenough to prevent leak off into the reservoir. In addition, the fluidvelocity and rheological properties must support solids suspension andtransport.

It is known that the bottom hole pressure of a wellbore declines as thereservoir matures, thereby complicating the wellbore cleanout. Forexample, if the fluid being pumped into the wellbore exits the workstring (e.g., coiled tubing) at an excessive pressure, the fluid mayenter the formation instead of returning to the surface with the sandparticulates.

To overcome this problem, it is known to utilize gasification (e.g., bythe addition of nitrogen to the fluid) to decrease the hydrostaticpressure in the wellbore. Thus, the fluid may be pumped at reducedbottom hole pressures and circulation through the wellbore may berestored to transport the particulates to the surface. However, overtime, the reservoir pressure may decline to a point whereby gasificationfails to result in consistent circulation of fluid to effectively removethe particulates.

Reverse circulating is another method commonly used to increase thetransport velocity of the fluid, especially when employing smalldiameter tubing in large wellbores.

Yet another prior art method of removing the particulate solids in thewellbore where the bottomhole circulating pressure is a concern employsa jet pump. In the oil and gas industry, the jet pump concept often isused to draw wellbore fluids into a closed circuit hydraulic stream andreturn the wellbore fluid to the surface. This procedure is generallyperformed in wells that have very low bottom hole pressures, where thewellbore fluids cannot be transported easily to the surface using othernitrogen lift methodologies to lighten the hydrostatic head of the well.As described in U.S. Pat. No. 5,033,545 to Sudol, issued Jul. 23, 1991,incorporated by reference herein in its entirety, the jet pump isdesigned such that well fluids and solids enter the jet pump at thebottom hole pressure (BHP). The jet pump then increases the fluidpressure as it pumps the fluids up the work string with the solidparticulates entrained in the fluids. Thus circulation is facilitated,as the circulation no longer depends on BHP alone.

FIG. 1 shows an exemplary prior art jet pump apparatus and method foreffectively removing particulates such as sand from within a wellboreusing production tubing. With reference to FIG. 1, a power fluid (arrowsPF) is admitted under pressure to an annular space between an outer pumpcasing 12 and the jet pump device body 5. The annular space is closedoff at its lower end. In the general installation shown in FIG. 1,tubing string 8 is attached at the top of the jet pump device body 5.

The jet pump includes one or several power fluid inlet ports 9 foradmitting power fluid to the main nozzle I of the pump. The main nozzle1 discharges into a throat area 100 of the pump assembly. The jet pumpalso includes a well fluids inlet port 7 for admitting well fluids, or amixture of fluids and solids, to fluid passages in fluid communicationwith throat area 100. Power fluid, under high pressure in the annularspace, flows in the direction of the arrows PF through the power fluidinlet port 9 into the main nozzle 1. The main nozzle 1 jets the powerfluid into the high impact area 2 of the throat area 100.

Well fluids and solids flow under formation pressure through the wellfluids inlet port 7. The well fluids and solids then flow in thedirection of the arrows WF and into the high impact area 2 of the throatarea 100. The well fluids and solids violently mix with the power fluidin the throat area 100, particularly in the high impact area 2. Thereturns (arrows R), comprised of power fluid, well fluids and solids,then move through the throat to production tubing 8, which extends tothe production equipment at the surface.

The jet pump also is particularly well-suited for use with a coiledtubing string inside a coiled tubing string, or “coil-in-coil tubing”(CCT), as described in U.S. Pat. No. 5,638,904 by Misselbrook et al.,issued Jun. 17, 1997, incorporated by reference herein in its entirety.The power fluid is pumped down the inner coiled tubing string, and thereturn fluid stream, which is comprised of a mixture of power fluid andwell fluids and solids, is taken up the coiled tubing-coiled tubingannulus.

The following is a simplified summary of the operation of this prior artapparatus and method. With reference to FIG. 2, a jet pump 5 is shownwithin a wellbore. The jet pump 5 is attached to the bottom of CCT (notshown) via housing 6. In operation, the jet pump closed circuithydraulic stream generally begins with power fluid, preferably water orbrine, being injected into a pipe with one end at the surface,preferably the inner coiled tubing string (from left to right in FIG.2). The power fluid then travels down the pipe to the wellbore, goesthrough jet pump 5 to entrain wellbore fluid, and finally returns tosurface through an alternate pipe or other closed path (pipe-pipeannulus), preferably the coiled tubing-coiled tubing annulus.

The power fluid enters the lower end of jet pump 5 in the directionshown by the arrows PF (from right to left in FIG. 2). As the powerfluid passes through nozzle 1 at nozzle exit 3, the velocity of thepower fluid increases significantly, creating a jet stream. The jet pumpitself acts like a venturi by taking the high pressure power fluid(pumped from surface) and increasing the power fluid's velocity via thenozzle 1. This increased velocity reduces the pressure in the powerfluid stream, which enables the low pressure power fluid stream to drawin some portion of the well fluids and solids (indicated by arrows WF)at well fluids inlet port 7. The high-velocity combined fluid stream,which may contain both fluids and solids, then enters the entrance endof the diffuser or throat area 100. As the combined fluid stream (arrowR) continues to travel upward through the throat area 100, the diameterof the throat increases, the velocity of the fluid decreases, and thefluid pressure increases. This recovered fluid pressure drives thereturn fluid stream (arrow R) back to the surface, overcoming thehydrostatic head.

If the jet pump is used to draw in sand or other well solids as part ofthe wellbore fluids, severe erosion in the throat area is observed, asthe high velocity power fluid stream causes the solids to impinge,scrape, and abrade the throat. As the solids initially are drawn intothe high velocity power fluid stream, the velocity of the solids-ladenedfluid does not yet match the velocity of the power fluid stream. Thesolids-ladened fluids tend to remain on the periphery of the power fluidstream, as shown in FIG. 3, where they are more likely to havehigh-velocity impact with the entrance section 10 of the throat 100. Ithas been determined that in many applications, this causes excessiveerosion in the high impact area 2.

As a practical matter, poor erosion performance translates intooperational inefficiencies, as more frequent trips out of and into holeare required to replace the excessively eroded components.

Erosion of the downhole tools may be exasperated when cleaningparticulates from deeper wells. Deeper wells produce additionalchallenges for the above-referenced procedure, as the deeper wells haveincreased hydrostatic pressure and increase friction pressure. Thus, thecoiled tubing operation must incorporate higher pump output pressure andhigher jet velocities in the nozzle and throat. For example, it is notuncommon for an 8600-foot well to have a bottom hole pressure of 1000pounds per square inch, causing the flow velocity through the throat tobe between 200 and 600 feet per second. These higher particle-laden jetvelocities increase the erosion rate in the throat.

It is also known in the prior art to decrease the erosion of thecomponents of downhole tools by manufacturing the components of variousmaterials, such as ceramics like Yttria stabilized zirconia, or 6%submicron tungsten carbide. However, these prior art methods fail toprovide the desired level of erosion performance and may not beeconomically feasible with deeper wells (and the concomitant increasedjetting velocities), as excessive erosion still may result.

Thus, there is a need for a method for improving erosion resistance(i.e., decreasing the erosion) of components used in the cleaning of awellbore, such as throats or diffusers utilized downhole, when thecomponents are exposed to high velocity sand/fluid slurries. The methodaccording to one embodiment of the invention resists erosion associatedwith the high velocity jets of solids-ladened fluid slurries generatedwhen removing particulate solids, such as sand, from the wellbore duringwell intervention or workover. Further, the method of a preferredembodiment improves longevity of components for downhole jet pumps andreduces the relative frequency of trips in and out of hole for worncomponent replacement.

SUMMARY OF THE INVENTION

The invention relates to methods of improving the erosion resistance(i.e. decreasing the erosion) of components—for example, throats anddiffusers—of downhole tools used in the removal of particulate solidsfrom the wellbore.

The preferred method comprises operating a jet pump in a condition knownas cavitation when drawing in sand or other wellbore solids, in order todecrease the erosive effect of drawing the solids into the jet pump.When a jet pump is operated in cavitation mode, the pumped power fluidstream velocity is increased to a point where the power fluid pressurebecomes very low or near absolute zero—lower than the vapor pressure ofthe fluid itself—where the fluid stream exits the nozzle. As the powerfluid exits the nozzle at this high velocity, the ultra low fluidpressure causes the power fluid to create cavitation vapor bubbles,which quickly form and then collapse as the power fluid is recaptured bythe throat. This action is extremely violent and causes severe mixing ofthe power fluid and the wellbore fluids being drawn in. The severemixing action forces the sand particles or other solids to be fullyimmersed in the fluid stream and lessens the sand particles' exposure tothe throat surface, thereby reducing erosion of the throat.

One embodiment of the invention is directed to a method of protecting ajet pump throat from downhole erosion comprising the steps ofpositioning a jet pump in a wellbore, pumping a power fluid through thejet pump at a sufficient velocity to cause the power fluid pressure inthe area between the nozzle and throat to be less than or equal to thepower fluid vapor pressure, and drawing solids-ladened wellbore fluidinto the jet pump and mixing the wellbore fluid with the power fluid.Another embodiment describes a method of removing solids from a wellborecomprising the steps of providing a jet pump in a wellbore, pumping apower fluid through the jet pump at a sufficient velocity to createcavitation vapor bubbles in the power fluid in the throat, and drawingsolids from the wellbore through the well fluid inlet ports and mixingthe solids with the cavitation vapor bubbles of the power fluid. Yetanother embodiment describes a method of removing solids from a wellborecomprising the steps of pumping a power fluid to a downhole jet pump,drawing wellbore solids into the jet pump and mixing the solids with thepower fluid while the fluid pressure of the power fluid is less than orequal to the vapor pressure of the power fluid, and transporting thesolids-ladened mixture through the throat of the jet pump and out of thewellbore.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a jet pump known in the prior art.

FIG. 2 shows a jet pump known in the prior art attached to coil-in-coiltubing.

FIG. 3 illustrates the erosive effects of operating a jet pump accordingto prior art methods.

FIG. 4 illustrates the operation of a jet pump in the cavitation mode inaccordance with one embodiment of the invention.

While the invention is susceptible to various modifications andalternative forms, a specific embodiment has been shown by way ofexample in the drawings and will be described in detail herein. However,it should be understood that the invention is not intended to be limitedto the particular forms disclosed. Rather, the intention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the invention as defined by the appended claims.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

An illustrative embodiment of the invention is described below as itmight be employed in the oil and gas recovery operation. In the interestof clarity, not all features of an actual implementation are describedin this specification. It will of course be appreciated that in thedevelopment of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure. Further aspects and advantages of the variousembodiments of the invention will become apparent from consideration ofthe following description and drawings.

Embodiments of the invention will now be described with reference to theaccompanying FIG. 4. Dimensions described or shown are intended forexample only, as the invention disclosed herein is not limited thereto.The invention is particularly well-suited for use with a downhole jetpump attached to coil-in-coil tubing. Referring to FIG. 4, the entrancesection 10 of a throat 100 is shown. The throat 100 may be comprised ofany hardened material suitable for downhole use, such as 6% cobalttungsten carbide. Flow of fluid during the cleanout procedure is fromright to left (i.e. the surface equipment is on the left, and thedownhole obstruction being removed from the wellbore is on the right). Amain nozzle I also is shown. By way of example, the inner diameter ofthe nozzle preferably is in the range of about 0.060 inch to 0.125 inch.

In operation (as illustrated generally in FIGS. 1 and 2), thehigh-velocity fluid with sand or other solid particulates ultimatelyenters the entrance section 10 of the throat 100. As shown schematicallyin FIG. 4, operating the jet pump in cavitation mode causes solids toenter the center of the throat passage, suspended in a mixture, andgreatly reduces the degree of erosional solids contact with the highimpact area 2.

First, the power fluid (arrows PFY preferably brine but alternativelywater, friction reduced water, gelled water, diesel, hydraulic oil, orthe like-enters the nozzle 1 at high static pressure and low velocity.Second, the power fluid (arrows PF) in a preferred embodiment exits thenozzle 1 at the nozzle exit 3 at high velocity and very lowpressure-near absolute zero and lower than the vapor pressure of thepower fluid itself. This ultra low fluid pressure at the nozzle exit 3causes the power fluid to vaporize and the creation of cavitation vaporbubbles. Third, solids-ladened well fluids (arrows WF) enter thewellbore under formation pressure at well fluids inlet 7. As the wellfluids and solids enter the power fluid stream, the power fluid velocitydecreases and the static pressure increases, thereby causing thecavitation vapor bubbles to recollapse as the power fluid is recapturedby the throat 100. The cavitation vapor bubble formation-and-recollapseaction is extremely violent and causes severe mixing of the power fluid(arrows PF) and the wellbore fluids (arrows WF) being drawn in. Asdepicted schematically in FIG. 4, the severe mixing action forces thesolids to be fully immersed in the combined return fluid stream (arrowR). This full immersion of the solids causes the solids to enter thecenter of the throat passage, thereby lessening the solids' directcontact with the internal walls of the throat entrance at high impactarea 2. As a result, erosion of the throat 100 is reduced. Operating thejet pump using the cavitation method of the present invention is thus animprovement over prior art methods having no or inferior erosionresistance.

Operating a jet pump in cavitation mode provides a maximum limit on thewellbore flow rate. Maximum wellbore flow rate is a function of multipleparameters, including nozzle diameter, throat diameter, and wellborepressure, as well as pump pressure and pump rate. After achieving themaximum wellbore flow rate, an additional increase in the pump rateachieves no incremental increase in returns at the surface. Therefore,whether a jet pump is operating in cavitation mode downhole may bedetermined at the surface by the presence of further increases in pumppressure and pump rate without achieving more suction or an increase inreturns.

For example, initially the jet pump may operate at a pump rate of 60liters per minute (lpm), with fluid returning to the surface at the samerate of 60 lpm. As the pump rate is increased, e.g. to 61 lpm, the fluidreturn rate may increase as more wellbore fluid is drawn into the returnfluid stream, e.g. to 62 lpm. If the pump rate is increased further,e.g. to 70 lpm, the fluid return rate may increase further, e.g. to 90lpm. The difference between the fluid return rate (out of system) of 90lpm and the pump rate (into system) of 70 lpm is 20 lpm, which indicatesthat the system yields an additional 20 lpm in suction. Now, if the pumprate is increased further to 80 lpm, and the fluid return rate is 100lpm, the net system increase would remain at 20 lpm in suction. Becausefurther increases in pump rate do not achieve an increase in suction orfluid returns, the system is operating at its maximum, and it may bededuced from the surface that the jet pump is operating in cavitationmode downhole.

Experimental results have been obtained for this embodiment of thepresent invention. A test was set up wherein a jet pump was operated incavitation mode to draw a sand/water slurry from a simulated wellbore.The erosion rate of the throat, which is proportional to thecross-sectional area of throat removed per volume of sand removed fromthe well, was approximately 50% of normal wear when the jet pump is notoperated in cavitation mode. Representative experimental data areprovided in TABLE 1 below. TABLE 1 Experimental Data Test # 044 Test #034 Test # 044 (continued) Measured Parameter Jul. 10, 2003 Oct. 9, 2003Oct. 15, 2003 Setup Nozzle diameter (in) 0.070 0.070 0.070 Throatdiameter (in) 0.102 0.102 0.102 Flow Rates Nozzle flow rate (LPM) 44 5151 Diffuser flow rate (LPM) 50 67 67 Wellbore flow rate (LPM) 6 16 (max)16 (max) Pressures Nozzle pressure (psi) 7600 9500 9500 Diffuserpressure* (psi) 4500 4500 4500 Wellbore pressure (psi) 1000 1000 1000Suction pressure (estimated 900 0 (cavitation) 0 (cavitation) psi) SandRemoval Results Volume of sand removed 6200 5750 13000 “SR” (in³) Wornthroat diameter (in) 0.113 0.107 0.115 Cross sectional area of 0.001860.00082 0.00222 throat removed “Area” (in²) Ratio SR/Area × 1000 (in)3330 7000 5860 Comments Low suction Pump at Realize flow rate cavitationto cavitation maximize erosion benefit sand intake*Diffuser pressure of 4500 psi is required for operations at 9,000 feettotal vertical depth (TVD).

Sand was removed from a simulated well of 9,000-foot total verticaldepth in conventional and cavitation modes of operation. Simulated wellconditions included a jet pump assembly with a nozzle of 0.070-inchdiameter, a throat of 0.102-inch diameter, and a throat configurationhaving a 5-micron thick layer of polycrystalline diamond (PCD).

The erosion of the throat 100 using the cavitation jet pump operationalmode of the present invention was compared to the erosion of the throat100 using the conventional jet pump operational mode. Operating the jetpump in cavitation mode allowed sand removal for a longer period thanconventionally. The experimental data suggests a 50% to 150% improvementin downhole component longevity due to a 50% to 150% improvement inerosion performance. These improvements suggest a corresponding increasein operational efficiency by way of a reduced need for frequent trips inand out of hole.

Although various embodiments have been shown and described, theinvention is not so limited and will be understood to include all suchmodifications and variations as would be apparent to one skilled in theart. Specifically, the erosion-decreasing method disclosed herein may bebeneficially employed by pumping the power fluid through the jet pump ata sufficient velocity to cause the power fluid pressure in the areabetween the nozzle and throat and/or in the throat itself to be lessthan or equal to the power fluid vapor pressure. Similarly, cavitationvapor bubbles in the power fluid may be created in the area between thenozzle and throat and/or in the throat itself. In addition, the wellborefluid and power fluid may be mixed while the fluid pressure is less thanor equal to the power fluid vapor pressure or shortly before the fluidpressure drops to the power fluid vapor pressure or immediately afterthe cavitation bubbles of the power fluid are recaptured.

1. A method of protecting a jet pump throat from downhole erosioncomprising the steps of: positioning a jet pump in a wellbore, the jetpump comprising a nozzle and a throat; pumping a power fluid through thejet pump at a sufficient velocity to cause the power fluid pressure inthe area between the nozzle and throat to be less than or equal to thepower fluid vapor pressure; and drawing solids-ladened wellbore fluidinto the jet pump and mixing the wellbore fluid with the power fluid. 2.The method of claim I further comprising mixing the wellbore fluid andpower fluid while the fluid pressure is less than or equal to the powerfluid vapor pressure.
 3. The method of claim 1 further comprisingpumping the power fluid through the jet pump at a sufficient velocity tocause the power fluid pressure in the throat to be less than or equal tothe power fluid vapor pressure.
 4. The method of claim 1 furthercomprising transporting the mixture of power fluid and solids-ladenedwellbore fluid through the throat of the jet pump and out of thewellbore.
 5. The method of claim 1 whereby the jet pump is positioned inthe wellbore by attaching the jet pump to a coil-in-coil tubing stringand running the jet pump on the coil-in-coil tubing into the wellbore.6. The method of claim 5 further comprising delivering the power fluidto the jet pump via the center tubing of a coil-in-coil tubing string.7. The method of claim 5 further comprising returning the mixture ofpower fluid and solids-laden wellbore fluid to the surface via the coiltubing-coil tubing annulus.
 8. The method of claim 1 wherein the powerfluid pressure at the nozzle exit is about absolute zero.
 9. The methodof claim 1 wherein the power fluid is selected from brine, water,friction reduced water, gelled water, diesel, or hydraulic oil.
 10. Amethod of protecting a jet pump throat from downhole erosion comprisingthe steps of: providing a jet pump in a wellbore, the jet pumpcomprising a nozzle, one or more well fluid inlet ports, and a throat;and pumping a power fluid through the jet pump at a sufficient velocityto create cavitation vapor bubbles in the power fluid in the throat; anddrawing solids-ladened wellbore fluid through the well fluid inlet portsand mixing the wellbore fluid with the power fluid.
 11. The method ofclaim 10 further comprising mixing the cavitation vapor bubbles in thepower fluid with the wellbore fluid.
 12. The method of claim 10 furthercomprising pumping the power fluid through the jet pump at a sufficientvelocity to create cavitation vapor bubbles in the area between thenozzle and throat.
 13. The method of claim 10 further comprisingtransporting the mixture of power fluid and solids-ladened wellborefluid through the throat of the jet pump and out of the wellbore. 14.The method of claim 10 wherein the power fluid is selected from brine,water, friction reduced water, gelled water, diesel, or hydraulic oil.15. The method of claim 10 further comprising attaching the jet pump toa coil-in-coil tubing string and positioning the jet pump at a desiredlocation in the wellbore.
 16. The method of claim 10 further comprisingdelivering the power fluid to the jet pump via the center tubing of acoil-in-coil tubing string.
 17. The method of claim 16 furthercomprising pumping the fluid mixture to the surface via the coiltubing-coil tubing annulus.
 18. The method of claim 10 wherein the powerfluid pressure at the nozzle exit is about absolute zero.
 19. A methodof protecting a jet pump throat from downhole erosion comprising thesteps of: positioning a jet pump in a wellbore, the jet pump comprisinga nozzle and a throat; pumping a power fluid through the jet pump at asufficient velocity to cause the suction pressure in the area betweenthe nozzle and throat to be less than or equal to the power fluid vaporpressure; drawing solids-ladened wellbore fluid into the jet pump andmixing the wellbore fluid with the power fluid; and transporting themixture of fluid out of the wellbore.
 20. A method of removing solidsfrom a wellbore comprising the steps of: positioning a jet pump in awellbore, the jet pump comprising a nozzle, a fluid inlet port and athroat; pumping a fluid through the jet pump at a sufficient velocity tocause the power fluid pressure in the area between the nozzle and throatto be less than or equal to the power fluid vapor pressure; and drawingsolids-ladened wellbore fluid into the jet pump through the fluid inletport and mixing the wellbore fluid with the power fluid.
 21. The methodof claim 20 further comprising mixing the wellbore fluid and power fluidwhile the fluid pressure is less than or equal to the power fluid vaporpressure.
 22. The method of claim 20 further comprising pumping thepower fluid through the jet pump at a sufficient velocity to cause thepower fluid pressure in the throat to be less than or equal to the powerfluid vapor pressure.
 23. The method of claim 20 further comprisingtransporting the mixture of power fluid and solids-ladened wellborefluid through the throat of the jet pump and out of the wellbore. 24.The method of claim 20 whereby the jet pump is positioned in thewellbore by attaching the jet pump to a coil-in-coil tubing string andrunning the jet pump on the coil-in-coil tubing into the wellbore. 25.The method of claim 24 further comprising delivering the power fluid tothe jet pump via the center tubing of a coil-in-coil tubing string. 26.The method of claim 25 further comprising pumping the fluid mixture tothe surface in the coil tubing-coil tubing annulus.
 27. The method ofclaim 20 where the jet pump is operated at a suction pressure of aboutabsolute zero.
 28. A method of removing solids from a wellborecomprising the steps of: providing a jet pump in a wellbore, the jetpump comprising a nozzle, one or more well fluid inlet ports, and athroat; pumping a power fluid through the jet pump at a sufficientvelocity to create cavitation vapor bubbles in the power fluid in thethroat; and drawing solids from the wellbore through the well fluidinlet ports and mixing the solids with the cavitation vapor bubbles ofthe power fluid.
 29. The method of claim 28 further comprising mixingthe cavitation vapor bubbles in the power fluid with the solids.
 30. Themethod of claim 28 further comprising transporting the mixture of powerfluid and solids through the throat of the jet pump and out of thewellbore.
 31. The method of claim 28 further comprising attaching thejet pump to a coil-in-coil tubing string and positioning the jet pump ata desired location in the wellbore.
 32. The method of claim 31 furthercomprising delivering the power fluid to the jet pump via the centertubing of a coil-in-coil tubing string.
 33. The method of claim 32further comprising transporting the solids to the surface in the coiltubing-coil tubing annulus.
 34. The method of claim 28 wherein the powerfluid pressure at the nozzle exit is about absolute zero.
 35. A methodof removing solids from a wellbore comprising the steps of: pumping apower fluid to a downhole jet pump; drawing wellbore solids into the jetpump and mixing the solids with the power fluid while the fluid pressureof the power fluid is less than or equal to the vapor pressure of thepower fluid, and transporting the solids-ladened mixture through thethroat of the jet pump and out of the wellbore.
 36. The method of claim35 whereby the jet pump is positioned in the wellbore by attaching thejet pump to a coil-in-coil tubing string and running the jet pump on thecoil-in-coil tubing into the wellbore.
 37. The method of claim 36further comprising delivering the power fluid to the jet pump via thecenter tubing of a coil-in-coil tubing string.
 38. The method of claim36 further comprising returning the mixture of power fluid and solids tothe surface via the coil tubing-coil tubing annulus.
 39. The method ofclaim 35 wherein the power fluid pressure at the nozzle exit is aboutabsolute zero.
 40. The method of claim 35 wherein the power fluid isselected from brine, water, friction reduced water, gelled water,diesel, or hydraulic oil.